1. Field of the Invention
The present invention relates to a squeegee roller for a liquid electrophotographic printer and, more particularly, to a squeegee roller for a liquid electrophotographic printer in which the roughness of a surface of an elastic rubber layer thereof is improved so that the efficiency of squeegeeing is improved.
2. Description of the Related Art
In general, a liquid electrophotographic printer, such as a color laser printer or a copier, produces a desired image by electrically attaching developer, which is a mixture of a solid toner having a predetermined color and a liquid carrier functioning as a solvent, to an area for an electrostatic latent image formed on a surface of a photoreceptor medium such as a photoreceptor web. A development unit for developing the developer in the area for an electrostatic latent image of the photoreceptor medium is provided in the printer.
Referring to FIG. 1, a development unit of the conventional liquid electrophotographic printer includes a development tray 12 for finally collecting developer D after being used for development, a development roller 14 arranged to maintain a predetermined distance of development gap G with respect to a photoreceptor web 10, a manifold 116 through which developer D is injected to the development gap G, a development container 13 for containing the collected developer D which is injected to the development roller 14, a development roller cleaning apparatus for removing the developer adhering to the outer circumferential surface of the development roller 14, and a squeegee roller 15 for making toner of the developer remaining on the photoreceptor web 10 a film and for separating carrier from the photoreceptor web 10.
The development roller cleaning apparatus rotates in contact with the development roller 14 and includes a brush roller 18, part of which is submerged in the developer D, and a blade 14b for removing foreign materials adhering to the surface of the development roller 14 which remain between the brush roller 18 and the development roller 14 after cleaning. Reference numeral 17 denotes a squeegee blade for squeegeeing developer while contacting a surface of the squeegee roller 15 in a drip-line removing mode after development.
FIG. 2 is a view for explaining the operation of the squeegee roller 15 which removes carrier. As shown in the drawing, after development, developer still remains between the photoreceptor web 10 and the squeegee roller 15. The remaining developer is referred to as a drip-line (DL). To remove the drip-line (DL), the blade 17 is allowed to contact the squeegee roller 15 and the circulating speed of the photoreceptor web 10 is reduced. In this state, a pressing force applied to the squeegee roller 15 contacting the photoreceptor web 10 is slightly reduced and the squeegee roller 15 is rotated in a direction reverse to the direction in which the photoreceptor web 10 circulates. Then, the drip line (DL) is removed and flows down along an outer circumferential surface of the squeegee roller 15. The developer is squeegeed by the blade 17 and falls into the developer tray 12.
However, the squeegee roller 15 is made by coating an elastic material around a metal core. There is no optimized specifications for the roughness of a surface thereof and the shape of a surface pattern. Thus, when the roughness of the surface of the squeegee roller 15 is less than or equal to 1.0 .mu.m, the surface of the squeegee roller 15 becomes too slippery. Then, as shown in FIG. 3, developer at A, B and C remaining on the photoreceptor web 10 flows in a direction reverse to a direction in which the photoreceptor web 10 proceeds, by the pressing force of the squeegee roller 15. Consequently, the printed image is deteriorated.
Meanwhile, when the roughness of the surface of the squeegee roller 15 is greater than or equal to 3.0 .mu.m, the surface of the squeegee roller 15 becomes too rough. Thus, the developer on the surface of the photoreceptor web 10 is not squeegeed by the squeegee roller 15 and continuously remains on the photoreceptor web 10. Therefore, the efficiency of squeegeeing is lowered.